The present invention relates to a ring laser gyroscope, and more particularly to an improved apparatus and method for calibrating and testing a ring laser gyroscope utilizing nonvolatile digital potentiometers to trim the control circuits of the ring laser gyroscope.
Ring laser gyroscope (RLG) devices for measuring angular rotation rates are known in the art. In these devices, two laser beams are generated in opposite directions around a closed loop path about the axis of rotation of the device. Rotation of the apparatus causes the effective path length for the two beams to change, thus producing a frequency difference between the two beams since the frequency of oscillation of the laser beams is dependent upon the length of the lasing path. The frequency difference between the beams causes a phase shift between the beams that changes at a rate proportional to the frequency difference. The interaction of the beams produces an interference fringe pattern which is observed to move with a velocity proportional to the rate of angular rotation of the device about the axis.
In order to ensure accurate operation of the ring laser gyroscope, a number of initial calibration steps must be performed. In particular, there are three calibrations that are especially important xe2x80x94the laser intensity monitor (LIM), the dithering motor, and the SIN A and SIN B gain circuits of the device. The LIM senses the output intensity of the laser utilized in the ring laser gyroscope, so as to provide a signal indicative of the relative health and remaining life of the laser. The dithering motor of the RLG is a mechanical device that oscillates the RLG at a predetermined frequency and with a predetermined range of angular rotation, known as a dither angle. Dithering of the RLG prevents an undesirable phenomenon known to those skilled in the art as xe2x80x9clock-inxe2x80x9d which hinders the operation of the RLG. The dither angle is calibrated specifically for each individual RLG to ensure proper operation. The operation of the RLG may be diagnostically evaluated by charting certain characteristics of the laser output in a lissajous pattern, as is known in the art. The shape of the lissajous pattern provides an indication of the phasing of the lasers utilized in the RLG as well as the general health of the lasers, and is best viewed when the SIN A and SIN B gain circuits are adjusted to reduce the gain of the circuit below the level of clamping of the signal producing the lissajous pattern.
All of the calibrations described above are labor-intensive processes that require a skilled technician to manually adjust certain components of the RLG to perform the required calibration. These manual adjustments typically necessitate breaking of the RLG""s seal, which then must be re-done after calibration with considerable expenditure of time and money. It would therefore be a significant improvement in the art to provide a mechanism for performing the required calibrations of ring laser gyroscopes automatically.
The present invention is a ring laser gyroscope (RLG) having control circuits that are capable of automatic calibration. The RLG generates two laser beams in opposite directions around a closed loop path to determine angular rotation of the RLG. The laser beams propagate in a laser gain medium, and a laser intensity monitor circuit is operatively connected to the laser gain medium to monitor an intensity of the laser beams propagating in the laser gain medium. A dithering circuit is provided, including a dithering motor for mechanically oscillating the RLG at a controlled frequency and dither angle. A gain circuit is operatively connected to a detector array of the RLG to amplify a detector signal therefrom. According to the present invention, an automatically variable resistance is provided to calibrate the laser intensity monitor circuit of the RLG, to control the dither angle at which the dithering motor mechanically oscillates the RLG, and/or to calibrate the gain circuit of the RLG. In one embodiment, the automatically variable resistance(s) is provided by one or more digital potentiometers connected to the relevant control circuitry.